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| United States Patent |
5,141,556
|
|
Matrick
|
August 25, 1992
|
Penetrants for aqueous ink jet inks
Abstract
An ink for ink jet printers which comprises an aqueous carrier medium,
pigment dispersion or dye and a diol penetrant. The latter is an aliphatic
diol having at least 6 carbon atoms, a solubility in water of at least 4.5
parts in 100 parts of water at 25.degree. C. and is selected from the
group consisting essentially of:
(1) compounds wherein at least 2 carbon atoms are attached as substituents
to the main chain, and
(2) Hexene [1,2-]diols.
The pigment dispersion consists of pigment particles and a dispersant,
preferably a polymeric dispersant having a hydrophilic segment and a
segment that links to the pigment. These inks exhibit rapid drying, are
storage stable, have reliable performance and give images having good
print quality.
| Inventors:
|
Matrick; Howard (Highlands, NJ)
|
| Assignee:
|
E. I. Du Pont de Nemours and Company (Wilmington, DE)
|
| Appl. No.:
|
714879 |
| Filed:
|
June 13, 1991 |
| Current U.S. Class: |
524/385; 106/31.58; 347/100; 524/269; 524/388 |
| Intern'l Class: |
C09D 011/02 |
| Field of Search: |
106/20,22,23
|
References Cited
U.S. Patent Documents
| 4170482 | Oct., 1979 | Mansukhani | 106/20.
|
| 4381946 | May., 1983 | Uehara et al. | 106/22.
|
| 4957553 | Sep., 1990 | Koike et al. | 106/20.
|
| 5006170 | Apr., 1991 | Schwartz et al. | 106/22.
|
Primary Examiner: Dixon, Jr.; William R.
Assistant Examiner: Klemanski; Helene
Claims
What is claimed is:
1. An aqueous ink jet ink composition comprising:
(a) an aqueous carrier medium,
(b) a pigment dispersion or dye; and
(c) an aliphatic diol penetrant compound having at least 6 carbon atoms, a
solubility in water of at least 4.5 parts in 100 parts of water at
25.degree. C., and selected from the group consisting of
(1) compounds wherein at least 2 carbon atoms are attached as substituents
to the main chain and represented by the general formula
C.sub.n H.sub.2n (OH).sub.2
wherein n is at least 6; and
(2) Hexene[1,2]diols.
2. The ink composition of claim 1 wherein the pigment dispersion comprises
a pigment and a polymeric dispersant.
3. The ink composition of claim 1 wherein n is 6-8.
4. The ink composition of claim 1 wherein at least 2 side chain or branched
carbon atoms are attached to the same main chain carbon atom.
5. The ink composition of claim 1 wherein the diol penetrant is a 1,3-diol
having the general formula:
##STR2##
wherein R is H or alkyl of 1-2 carbon atoms and R' is alkyl of 2-6 carbon
atoms.
6. The ink composition of claim 5 wherein R is --CH.sub.3 or --C.sub.2
H.sub.5, and R' is C.sub.2 H.sub.5 or C.sub.3 H.sub.7.
7. The ink composition of claim 6 wherein the diol penetrant is
2-ethyl-2-methyl-1,3-propanediol.
8. The ink composition of claim 6 wherein the diol penetrant is
2,2-diethyl-1,3-propanediol.
9. The ink composition of claim 6 wherein the diol penetrant is
2-methyl2-propyl-1,3-propanediol.
10. The ink of claim 1 wherein the diol penetrant is a 2,4- or 2,5-diol
having the general formula:
(CH.sub.3).sub.2 COH(CH.sub.2).sub.n COH(CH.sub.3).sub.2
wherein n=1-2.
11. The ink composition of claim 10 wherein the diol penetrant is
2,4-dimethyl-2,4-pentanediol.
12. The ink composition of claim 10 wherein the diol penetrant is
2,5-dimethyl-2,5-hexanediol.
13. The ink composition of claim 4 wherein the diol penetrant is
3,3-dimethyl-1,2-butanediol.
14. The ink composition of claim 1 or 2 wherein the diol penetrant is
5-hexene-1,2-diol.
15. The ink composition of claim 2 wherein the polymeric dispersant is an
AB or BAB block copolymer wherein
(a) the A segment is a hydrophobic homopolymer or copolymer of an acrylic
monomer having the formula:
CH.sub.2 =C(X)(Y)
wherein X is H or CH.sub.3 ; and Y is C(O)OR.sub.1, C(O)NR.sub.2 R.sub.3,
or CN, wherein R.sub.1 is an alkyl, aryl, or alkylaryl group having 1 to
20 carbon atoms, and R.sub.2 and R.sub.3 are hydrogen or an alkyl, aryl,
or alkylaryl group having 1 to 9 carbon atoms; said A segment having an
average molecular weight of at least approximately 300 and being water
insoluble; and
(b) the B segment is a hydrophilic polymer, or salt thereof, of
(1) an acrylic monomer having the formula
CH.sub.2 =C(X)(Y.sub.1),
wherein X is H or CH.sub.3 ; and Y.sub.1 is C(O)OH, C(O)NR.sub.2 R.sub.3,
C(O)OR.sub.4 NR.sub.2 R.sub.3 or C(OR.sub.5); wherein R.sub.2 and R.sub.3
are hydrogen or an alkyl, aryl, or alkylaryl group having 1 to 9 carbon
atoms; R.sub.4 is an alkyl diradical having 1 to 5 carbon atoms; and
R.sub.5 is an alkyl diradical having 1 to 20 carbon atoms and optionally
containing one or more hydroxyl or ether groups; or
(2) a copolymer of the acrylic monomer of (1) with an acrylic monomer
having the formula:
CH.sub.2 =C(X)(Y)
where X and Y are the substituent groups defined for the A segment; the B
segment having an average molecular weight of at least approximately
300,and being water soluble.
16. The pigmented ink of claim 15 wherein the polymeric dispersant is an AB
or BAB block copolymer wherein the A segment of said block copolymer is a
homopolymer or copolymer prepared from at least one monomer selected from
the group consisting of methyl methacrylate, ethylmethacrylate, propyl
methacrylate, butyl methacrylate, hexyl methacrylate, 2-ethylhexyl
methacrylate, octyl methacrylate, lauryl methacrylate, stearyl
methacrylate, phenyl methacrylate, benzyl methacrylate, hydroxyethyl
methacrylate, hydroxypropyl methacrylate, 2-ethoxyethyl methacrylate,
methacrylonitrile, 2-trimethylsiloxyethyl methacrylate, glycidyl
methacrylate, p-tolyl methacrylate, sorbyl methacrylate, methyl acrylate,
ethyl acrylate, propyl acrylate, butyl acrylate, hexyl acrylate,
2-ethylhexyl acrylate, octyl acrylate, lauryl acrylate, stearyl acrylate,
phenyl acrylate, benzyl acrylate, hydroxyethyl acrylate, hydroxypropyl
acrylate, acrylonitrile, 2-trimethyl-siloxyethyl acrylate, glycidyl
acrylate, p-tolyl acrylate, and sorbyl acrylate.
17. The ink composition of claim 16 wherein the A segment of said block
copolymer is a homopolymer or copolymer prepared from methyl methacrylate,
n-butyl methacrylate, 2-ethylhexyl methacrylate or a copolymer ethyl
methacrylate with butyl methacrylate.
18. The ink composition of claim 17 wherein the A segment is n-butyl
methacrylate.
19. The ink composition of claim 15 wherein the B segment of said block
copolymer is a homopolymer or copolymer prepared from at least one monomer
selected from the group consisting essentially of methacrylic acid,
acrylic acid, dimethylaminoethyl methacrylate, diethylaminoethyl
methacrylate, t-butylaminoethyl methacrylate, dimethylaminoethyl acrylate,
diethylaminoethyl acrylate, dimethylaminopropyl methacrylamide,
methacrylamide, acrylamide, and dimethylacrylamide.
20. The ink composition of claim 19 wherein the B segment of said block
copolymer is a polymer of methacrylic acid or dimethylaminoethyl
methacrylate.
21. The ink composition of claim 20 wherein the B segment of said block
copolymer is a homopolymer polymer of methacrylic acid.
22. The ink composition of claim 20 wherein said ink contains approximately
0.1 to 15% pigment, 0.1 to 30% block copolymer, and 70 to 99.8% aqueous
carrier medium plus penetrant, based on the weight of the total ink
composition.
23. The ink composition of claim 22 wherein the aqueous carrier medium
comprises water and at least one water soluble organic solvent.
24. The ink composition of claim 23 wherein aqueous carrier medium plus
penetrant contains from 30% water/70% solvent/penetrant mixture to 95%
water/5% solvent/penetrant mixture, based on the total weight of the
aqueous carrier medium plus penetrant.
25. The ink composition of claim 24 wherein the solvent/penetrant mixture
contains 15-95% penetrant, based on the weight of the solvent/penetrant
mixture.
26. The ink composition of claim 25 wherein the solvent/penetrant mixture
contains 25-75% penetrant, based on the weight of the solvent/penetrant
mixture.
27. The ink composition of claim 22 wherein said ink contains approximately
0.1 to 8% pigment, 0.1 to 8% block copolymer, and 94 to 99.8% aqueous
carrier medium plus penetrant, based on the weight of the total ink
composition.
28. The ink composition of claim 15 wherein the A segment of said block
copolymer is a polymer of methyl methacrylate, butyl methacrylate, or
2-ethylhexyl methacrylate and the B segment is a polymer of methacrylic
acid or dimethylaminoethyl methacrylate.
29. The ink composition of claim 15 wherein the B segment(s) constitute
approximately 25 to 65%, by weight, of said block copolymer.
30. The ink composition of claim 1 wherein said ink contains approximately
0.2 to 20% dye, and 80 to 99.8% aqueous carrier medium plus penetrant,
based on the weight of the total ink composition.
31. The ink composition of claim 30 wherein said aqueous carrier medium
plus penetrant contains 15-95% penetrant based on the weight of the
aqueous carrier medium plus penetrant.
32. The ink of claims 1 or 2 wherein the aqueous carrier medium is a
mixture of water and at least one water soluble organic solvent having at
least 2 hydroxyl groups.
33. The ink composition of claim 2 wherein the pigment particles have a
median particle size of approximately 0.01 to 1 micron.
34. The ink composition of claim 2 wherein the polymeric dispersant is
neutralized with a neutralizing agent selected from the group consisting
of organic bases, alkanolamines, alkali metal hydroxides, and mixtures
thereof.
35. An ink composition of claims 1 or 2 wherein a surfactant is present.
36. An ink composition of claim 35 wherein the surfactant is a
polyalkyleneoxide modified polydimethylsiloxane.
Description
FIELD OF THE INVENTION
This invention relates to aqueous inks for ink jet printers, and, more
particularly, to aqueous, colored inks containing penetrants.
BACKGROUND OF THE INVENTION
Ink jet printing is a non-impact method for recording information in
response to an electronic signal, such as that generated by a computer. In
the printer the electronic signal produces droplets of ink that are
deposited on a substrate such as paper or transparent film. Ink jet
printers have found broad commercial acceptance due to their reliability,
relatively quiet operation, graphic capability, print quality and low
cost. Thermal or bubble jet drop-on-demand printers have been especially
successful and have found broad application as output for personal
computers in the office and the home.
Both dyes and pigments have been used as ink colorants for ink jet
printers. However, dyes have several disadvantages. They are water-soluble
and remain so after drying. They are redissolved by contact with water and
will run when exposed to a water spill. Also dye images smear on contact
with felt pen markers. In addition they exhibit poor light stability
relative to pigments and are known to fade even under conditions of office
fluorescent lighting. Thus, there are several disadvantages with the use
of dye-based ink jet inks, many of which prohibit their use in
applications requiring moisture resistance and greater light stability.
Pigments can be used as ink colorants for ink jet printers. Pigment-based
inks contain cosolvents which provide improved water and smear resistance
and improved lightfastness compared to dyes. However, the presence of
these cosolvents which include penetrants also tends to destabilize
pigment dispersions. Thus, pigments are a useful alternative to dyes
provided the pigment dispersions can be made stable to flocculation and
settling.
Three major concerns dominate ink jet ink technology. They are (1) the
drying rate, (2) print quality, and (3) reliability. Drying rate
determines the throughput rate and therefore productivity.
One major deficiency of thermal ink jet printers is their relatively slow
printing speed compared to printers using competing technologies. A major
obstacle is the ink drying rate. In a sheet fed printer, the ink must be
dry before the succeeding sheet contacts it or the ink will smear.
Drying occurs by both evaporation and penetration. Evaporation is
determined by solvent vapor pressure whereas penetration is determined by
interfacial energy between the ink and the paper and the porosity of the
print media. The use of penetrants is known in the art as a means to
increase the rate of penetration of inks. However, the known penetrants
such as Butyl Carbitol.RTM., cause pigment dispersions to flocculate and
therefore cannot be used in pigmented ink jet inks.
Water-based pigment dispersions are well known in the art, and have been
used commercially for applying films, such as paints, to various
substrates. The pigment dispersion is generally stabilized by either a
non-ionic or ionic technique. Ink jet inks containing pigment dispersions
stabilized with AB or BAB block copolymers are also known.
Print quality is defined by factors such as optical density, edge
acuity/feathering, spray and other artifacts, dots/square inch, and drop
volume. Some reliability issues are decap or crust time which is defined
as the time span over which a pen can be exposed to the atmosphere without
failing to print, storage stability of the ink as seen by physical or
chemical changes, compatibility with equipment material, and robustness
towards variability in firing conditions.
The three major concerns discussed above often compete with one another.
For example, methods for decreasing drying rate will adversely affect
either print quality or reliability. Using a more volatile cosolvent will
decrease drying time but also decrease decap time.
Accordingly, a need exists for penetrants that will increase ink drying
without destabilizing pigment-based inks.
The cosolvents or penetrants of this invention are able to increase
penetration thereby decreasing drying rate without decreasing pigment
dispersion stability or reduce decap time. In addition the penetrants of
this invention provide maximum penetration and spreading which is highly
desirable in a small drop volume ink cartridge.
A major advantage of the use of the penetrants claimed in this invention is
rapid media penetration along with compatibility with aqueous pigment
dispersions. The penetrants, however, are also useful in dye-based inks.
SUMMARY OF THE INVENTION
The invention relates to an aqueous ink jet ink composition comprising:
(a) an aqueous carrier medium,
(b) a pigment dispersion or dye; and
(c) an aliphatic diol penetrant compound having at least 6 carbon atoms, a
solubility in water of at least 4.5 parts in 100 parts of water at
25.degree. C., and selected from the group consisting essentially of
(1) compounds wherein at least 2 carbon atoms are attached as substituents
to the main chain, and
(2) Hexene [1,2-] diols.
The inks of the invention are extremely stable, have low viscosity, exhibit
excellent print quality, provide excellent smear resistance after drying
and acceptable crusting time. They may be used with a variety of ink jet
printers such as continuous, piezoelectric drop-on-demand and thermal or
bubble jet drop-on-demand, and are particularly adapted for use in thermal
ink jet printers.
DETAILED DESCRIPTION OF THE INVENTION
The invention relates to an ink jet ink composition which is particularly
suited for use in ink jet printers in general, and thermal ink jet
printers in particular. The ink jet ink composition encompasses both
pigmented-based inks and dye-based inks. The pigmented inks comprise an
aqueous carrier medium, a diol penetrant and a pigment dispersion which is
an aqueous dispersion of pigment particles, stabilized by polymeric
dispersants, that are stable over long periods, both in storage and in the
printer. The dye-based inks comprise an aqueous carrier medium, a dye and
a diol penetrant. The inks may be adapted to the requirements of a
particular ink jet printer to provide a balance of light stability, smear
resistance, viscosity, surface tension, high optical density, and crust
resistance.
The aqueous carrier may contain an organic water soluble compound other
than the penetrant as well as water.
Diols of less than 6 carbon atoms are water soluble but do not promote
penetration (see Control 5, Examples, Neopentyl Glycol).
Diols with too many carbon atoms may be effective penetrants but can
destabilize the pigment dispersions and are likely to be insoluble in the
aqueous ink. This can be illustrated as follows:
______________________________________
Water Stability
Penetrant Solubility delta nm
______________________________________
2-Ethyl-1,3- 4.2% at 20.degree. C..sup.(a)
42
hexanediol
1,2,4-Trimethyl-
1.9% at 25.degree. C..sup.(a)
60
1,3-pentanediol
2,2-Diethyl- 25% at 20.degree. C..sup.(a)
17
1,3-propanediol
______________________________________
.sup.(a) Industrial Solvent Handbook, E. W. Flock, 3rd Edition, Noyes Dat
Corp., Park Ridge NJ
All three compounds are effective penetrants, but the first two cause
excessive aggregation/flocculation upon storage and are not useable in
pigmented inks. They both have solubilities in water of less than 4.5%. A
change in aggregate size of less than 20 nm is considered acceptable
stability (see Table 3, Examples).
It is important that the penetrant be substantially soluble at the level of
use, i.e., if the ink formulation requires 5% of the penetrant to obtain
useful penetration rates, then the penetrant must have a solubility nearly
equal to or greater than the penetrant use level. If the penetrant forms a
third phase in addition to the dispersed pigment and the aqueous phase,
then the pigment dispersion is likely to become unstable and settle during
storage. When a second organic cosolvent is present, a somewhat lower
solubility in water than the use level may be acceptable since the
presence of a second cosolvent promotes penetrant solubility.
PENETRANT OR COSOLVENT
The inks of the invention contain penetrants or cosolvents that are able to
decrease drying time without decreasing pigment dispersion stability or
decap time. The penetrants include aliphatic diol compounds having at
least 6 carbon atoms, a solubility in water of at least 4.5 parts in 100
parts of water at 25.degree. C., and selected from the group consisting
essentially of
(1) compounds wherein at least 2 carbon atoms are attached as substituents
to the main chain, and
(2) 1,2-Hexene diols.
Compounds included in (1) are those compounds wherein the carbon is part of
a single side chain or multiple side chains, for example,
2,2-dialkyl-1,3-diols. More specifically 2-ethyl-2-methyl-1,3-propane diol
is a compound where 3 carbon atoms on side chains are attached to the main
chain.
Alternatively, the penetrant compound may be an aliphatic diol with the
general formula:
C.sub.n H.sub.2n (OH).sub.2
wherein n is at least 6, preferably 6-8, and at least 2 carbon atoms are
attached as substituents to the main chain.
In one embodiment of (a) at least 2 carbon atoms are attached to the same
main chain carbon atom. However, as shown in the Comparative Examples of
Table 2, compounds such as hexylene glycol (control 4) which can be used
as part of the carrier medium, are not as effective as penetrants.
Some useful diol penetrants are disclosed below:
1) 2,2-Dialkyl-1,3-diols having the following formula:
##STR1##
wherein R is --H, --CH.sub.3 or --C.sub.2 H.sub.5, and R' is --C.sub.2
H.sub.5, --C.sub.3 H.sub.7 or --C.sub.4 H.sub.9.
Some specific 1,3-diols include:
______________________________________
Compound R R'
______________________________________
2-Ethyl-2-methyl- --CH.sub.3
--C.sub.2 H.sub.5
1,3-propanediol
2,2-Diethyl- --C.sub.2 H.sub.5
--C.sub.2 H.sub.5
1,3-propanediol
2-Methyl-2-propyl --CH.sub.3
--C.sub.3 H.sub.7
1,3-propanediol
______________________________________
2) Compounds in which at least one hydroxyl group of the diol are attached
to a secondary or tertiary carbon atom.
2a) 2,4- and 2,5-Diols having the following formula:
(CH.sub.3).sub.2 COH(CH.sub.2).sub.n COH(CH.sub.3).sub.2
wherein n=1-2.
Some specific 2,4- and 2,5-diols include:
______________________________________
Compound n =
______________________________________
2,4-Dimethyl-
1
2,4-pentanediol
2,5-Dimethyl-
2
2,5-hexanediol
______________________________________
2b) 3,3-Dimethyl-1,2-butanediol
2c) Hexene-1,2-diols of the general formula:
C.sub.6 H.sub.10 (OH).sub.2
A specific example of a hexene-1,2-diol is 5-hexene-1,2-diol.
A major advantage of using the penetrants described in this invention is
their compatibility with pigment dispersions. However, the penetrants can
also be used in dye-based ink to impart rapid penetration of aqueous
dye-based inks into the paper.
The pigment dispersion comprises a pigment and a dispersant, preferably a
polymeric dispersant.
POLYMERIC DISPERSANTS
Polymeric dispersants suitable for practicing the invention include AB or
BAB block copolymer wherein the A block is hydrophobic and serves to link
with the pigment, and the B block is hydrophilic and serves to disperse
the pigment in the aqueous medium. Selection of the polymer for a specific
application will depend on the selected pigment and aqueous medium. In
general, the polymer is an AB or BAB block copolymer wherein
(a) the A segment is a hydrophobic homopolymer or copolymer of an acrylic
monomer having the formula:
CH.sub.2 =C(X)(Y)
wherein X is H or CH.sub.3 ; and Y is C(O)OR.sub.1, C(O)NR.sub.2 R.sub.3,
or CN, wherein R.sub.1 is an alkyl, aryl, or alkylaryl group having 1 to
20 carbon atoms, and R2 and R3 are hydrogen or an alkyl, aryl, or
alkylaryl group having 1 to 9 carbon atoms; said A segment having an
average molecular weight of at least approximately 300 and being water
insoluble; and
(b) the B segment is a hydrophilic polymer, or salt thereof, of
(1) an acrylic monomer having the formula
CH.sub.2 =C(X)(Y.sub.1),
wherein X is H or CH.sub.3 ; and Y.sub.1 is C(O)OH, C(O)NR.sub.2 R.sub.3,
C(O)OR.sub.4 NR.sub.2 R.sub.3 or C(OR.sub.5); wherein R.sub.2 and R.sub.3
are hydrogen or an alkyl, aryl, or alkylaryl group having 1 to 9 carbon
atoms; R.sub.4 is an alkyl diradical having 1 to 5 carbon atoms; and
R.sub.5 is an alkyl diradical having 1 to 20 carbon atoms and optionally
containing one or more hydroxyl or ether groups; or
(2) a copolymer of the acrylic monomer of (1) with an acrylic monomer
having the formula:
CH.sub.2 =C(X)(Y)
where X and Y are the substituent groups defined for the A segment; the B
segment having an average molecular weight of at least approximately 300
and being water soluble.
The B block(s) generally will constitute 10 to 90%, preferably 25 to 65%,
of the entire block polymer by weight.
The A block is a polymer or copolymer prepared from at least one acrylic
monomer having the formula set forth above. The R.sub.1, R.sub.2 and
R.sub.3 groups optionally may contain hydroxy, ether, OSi(CH.sub.3).sub.3
groups, and similar substituent groups. Representative monomers that may
be selected include, but are not limited to, the following: methyl
methacrylate (MMA), ethyl methacrylate (EMA), propyl methacrylate, n-butyl
methacrylate (BMA or NBMA), hexyl methacrylate, 2-ethylhexyl methacrylate
(EHMA), octyl methacrylate, lauryl methacrylate (LMA), stearyl
methacrylate, phenyl methacrylate, benzyl methacrylate, hydroxyethyl
methacrylate (HEMA), hydroxypropyl methacrylate, 2-ethoxyethyl
methacrylate, methacrylonitrile, 2-trimethylsiloxyethyl methacrylate,
glycidyl methacrylate(GMA), p-tolyl methacrylate, sorbyl methacrylate,
methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hexyl
acrylate, 2-ethylhexyl acrylate, octyl acrylate, lauryl acrylate, stearyl
acrylate, phenyl acrylate, benzyl acrylate, hydroxyethyl acrylate,
hydroxypropyl acrylate, acrylonitrile, 2-trimethyl-siloxyethyl acrylate,
glycidyl acrylate, p-tolyl acrylate, and sorbyl acrylate. Preferred A
blocks are homopolymers and copolymers prepared from methyl methacrylate,
butyl methacrylate, 2-ethylhexyl methacrylate, or copolymers of methyl
methacrylate with butyl methacrylate.
The A block also may contain a hydrophilic monomer such as CH.sub.2
=C(X)(Y)', wherein X is H or CH.sub.3 and Y' is C(O)OH, C(O)NR.sub.2
R.sub.3, C(O)OR.sub.4 NR.sub.2 R.sub.3, C(OR.sub.5), or their salts,
wherein R.sub.2 and R.sub.3 may be H or C1 to C9 alkyl, aryl, or
alkylaryl, R.sub.4 is a C1 to C5 alkyl diradical, and R.sub.5 is a C1 to
C20 alkyl diradical which may contain hydroxy or ether groups, to provide
some changes in solubility. However, there should not be enough
hydrophilic monomer present in the A block to render it, or its salt,
completely water soluble.
The B block is a polymer prepared from at least one acrylic monomer having
the formula provided above. Representative monomers include methacrylic
acid (MAA), acrylic acid, dimethylaminoethyl methacrylate (DMAEMA),
diethylaminoethyl methacrylate, t-butylaminoethyl methacrylate,
dimethylaminoethyl acrylate, diethylaminoethyl acrylate,
dimethylaminopropyl methacrylamide, methacrylamide, acrylamide, and
dimethylacrylamide. Homopolymers or copolymers of methacrylic acid or
dimethylaminoethyl methacrylate are preferred.
The acid containing polymer may be made directly or may be made from a
blocked monomer with the blocking group being removed after
polymerization. Examples of blocked monomers that generate acrylic or
methacrylic acid after removal of the blocking group include:
trimethylsilyl methacrylate (TMS-MAA), trimethylsilyl acrylate,
1-butoxyethyl methacrylate, 1-ethoxyethyl methacrylate, 1-butoxyethyl
acrylate, 1-ethoxyethyl acrylate, 2-tetrahydropyranyl acrylate, and
2-tetrahydropyranyl methacrylate.
The B block may be a copolymer of an acid or amino containing monomer with
other monomers, such as those used in the A block. The acid or amino
monomer may be used in a range of 10 to 100%, preferable in a range of 20
to 100%, of the B block composition. The B block(s) generally will
constitute 10 to 90%, preferably 25 to 65%, of the entire block polymer by
weight.
Block copolymers that are useful in practicing the invention have a number
average molecular weight below 20,000, preferably below 15,000, and
typically in the range of 1,000 to 3,000. Preferred block copolymers have
number average molecular weights in the range of 500 to 1500 for each A
and B block.
Representative AB and BAB block polymers that may be selected include the
following, wherein the values recited represent the degree of
polymerization of each monomer. A double slash indicates a separation
between blocks and a single slash indicates a random copolymer. For
example, MMA//MMA/MMA 10//5/7.5 is an AB block polymer with an A block of
MMA that is 10 monomer units long, molecular weight of 1000 and a B block
that is a copolymer of MMA and MAA with 5 monomer units of MMA and 7.5
units of MAA; molecular weight of the B block is 1145.
______________________________________
MOL. WEIGHT
______________________________________
AB BLOCK POLYMER
EHMA//EHMA/MAA
3//3/5 1618
5//2.5/2.5 1700
5//5/10 2840
20//10/10 6800
15//11/22 7040
EHMA//LMA/MAA
10//10/12 5552
EHMA//MMA/EHMA/MAA
10//5/5/12 4502
EHMA//MMA/MAA
5//5/10 2350
5//10/10 2850
EHMA//MAA
15//5 3400
BMA//BMA/MAA
5//2.5/2.5 1280
10//5/10 3000
20//10/20 6000
15//7.5/3 3450
5//5/10 2300
5//10/5 2560
BMA//MMA/MAA
15//15/5 4060
15//7.5/3 3140
10//5/10 2780
MMA//MMA/MAA
10//5/10 2360
10//5/5 1930
10//5/7.5 2150
20//5/7.5 3150
15/7.5/3 2770
MMA//EHMA/MAA
5//5/10 2350
10//5/10 2850
BMA/MMA//BMA/MAA
5/5//5/10 2780
BMA//MAA
10//10 2260
BMA//HEMA/MAA
15//7.5/3 3360
7.5//7.5/3 2300
15//7.5/7.5 3750
BMA//BMA/DMAEMA
10//5/10 3700
BMA//BMA/DMAEMA/MAA
10//5/5/5 2635
BAB BLOCK POLYMER
BMA/MAA//BMA//BMA/MAA
5/10//10//5/10 4560
MMA/MAA//MMA//MMA/MAA
5/7.5//10//5/7.5 3290
______________________________________
Preferred block polymers are methyl methacrylate//methyl
methacrylate/methacrylic acid (10//5/7.5), 2-ethylhexyl
methacrylate//2-ethylhexyl methacrylate/methacrylic acid (5//5/10),
n-butyl methacrylate//n-butyl methacrylate/methacrylic acid (10//5/10),
n-butyl methacrylate//methacrylic acid (10//10)), ethylhexyl
methacrylate//methyl methacrylate/methacrylic acid (5//10/10),
n-butylmethacrylate//2-hydroxyethyl methacrylate/methacrylic acid
(5//10/10), n-butylmethacrylate//2-hydroxyethyl methacrylate/methacrylic
acid (15//7.5/3), methyl methacrylate//ethylhexyl methacrylate/methacrylic
acid (5//5/10), and butyl methacrylate//butyl
methacrylate/dimethylaminoethyl methacrylate (10//5/10).
To solubilize the B block into the aqueous medium, it may be necessary to
make salts of either the acid or amino groups contained in the B block.
Salts of the acid monomers can be made with the counter component being
selected from organic bases such as mono-, di-, tri-methylamine,
morpholine, n-methyl morpholine; alcohol amines such as
dimethylethanolamine (DMEA), methyldiethanolamine, mono-, di-, and
tri-ethanolamine; pyridine; ammonium hydroxide; tetra-alkylammonium salts
such as tetramethylammonium hydroxide, tetraethylammonium hydroxide;
alkali metals such as lithium, sodium and potassium, and the like.
Preferred neutralizing agents include dimethylethanolamine and sodium and
potassium hydroxides, with potassium hydroxide being particularly
preferred for inks to be used in thermal ink jet printers. Salts of the
amino monomers can be made with the counter component being selected from
organic acids such as acetic acid, formic acid, oxalic acid, dimethylol
propionic acid, halogens such as chloride, fluoride, and bromide, and
other inorganic acids, such as sulfuric acid, nitric acid, phosphoric acid
and the like. It is also possible to convert the amino group into a
tetra-alkyl ammonium salt. Amphoteric polymers, that is polymer that
contains both an acid group and an amino group, may be used as is or can
be neutralized with either addition of acid or base.
The AB and BAB polymers can be advantageously produced by stepwise
polymerization process such as anionic or group transfer polymerization as
described in Webster, U.S. Pat. No. 4,508,880, the disclosure of which is
incorporated herein by reference. Polymers so produced have precisely
controlled molecular weight, block sizes and very narrow molecular weight
distributions. The polymer typically has a dispersity less than 2,
generally in the range of 1.0 to 1.4. Dispersity is the polymer weight
average molecular weight divided by its number average molecular weight.
Number average molecular weight can be determined by gel permeation
chromatography (GPC). The AB or BAB block polymers may also be formed by
free radical polymerization wherein the initiation unit is comprised of
two different moieties which initiate polymerization at two distinctly
different temperatures. However, this method may cause contamination of
the block copolymers with homopolymer and coupled products.
The AB block polymers also may be prepared using conventional anionic
polymerization techniques, in which a first block of the copolymer is
formed, and upon completion of the first block, a second monomer stream is
started to form a subsequent block of the polymer. A low reaction
temperature (e.g., 0.degree. to -70.degree. C.) is maintained in this case
to minimize side reactions and form blocks of the desired molecular
weights.
With many of these techniques, and especially with the group transfer
polymerization process, the initiator may be non-functional, may contain
an acid group (used as is or in a blocked form) or may contain an amino
group. Either the hydrophobic A block or the hydrophilic B block may be
made first. The BAB block polymers also may be prepared by anionic
polymerization or group transfer polymerization techniques by first
polymerizing one of the B Blocks, then polymerizing the hydrophobic A
block, and then polymerizing the second B Block.
Random copolymers can be used as dispersants although not as effective in
stabilizing pigment dispersions. Amongst these may be mentioned
half-esters of maleic acid/styrene copolymers, lignin sulfonate
derivatives and copolymers of acrylic and methacrylic acid with styrene.
COLORANTS
Colorants useful in practicing the invention comprise both pigments and
dyes.
Pigments
Amongst pigments, a wide variety of organic and inorganic pigments, alone
or in combination, may be selected to make the ink. The term "pigment" as
used herein means an insoluble colorant. The pigment particles are
sufficiently small to permit free flow of the ink through the ink jet
printing device, especially at the ejecting nozzles that usually have a
diameter ranging from 10 micron to 50 micron. The particle size also has
an influence on the pigment dispersion stability, which is critical
throughout the life of the ink. Brownian motion of minute particles will
help prevent the particles from settling. It is also desirable to use
small particles for maximum color strength. The range of useful particle
size is approximately 0.005 micron to 15 micron. Preferably, the pigment
particle size should range from 0.005 to 5 micron, next preferably from
0.005 to 1 micron more preferably, from 0.005 to 0.3 micron and still more
preferably approximately 0.01-1 micron.
The selected pigment may be used in dry or wet form. For example, pigments
are usually manufactured in aqueous media and the resulting pigment is
obtained as water wet presscake. In presscake form, the pigment is not
aggregated to the extent that it is in dry form. Thus, pigments in water
wet presscake form do not require as much deaggregation in the process of
preparing the inks from dry pigments. Representative commercial dry
pigments that may be used in practicing the invention include the
following:
______________________________________
Color
Index
Pigment Brand Name Manufacturer
Pigment
______________________________________
Permanent Yellow DHG
Hoechst Yellow 12
Permanent Yellow GR Hoechst Yellow 13
Permanent Yellow G Hoechst Yellow 14
Permanent Yellow NCG-71
Hoechst Yellow 16
Permanent Yellow GG Hoechst Yellow 17
Hansa Yellow RA Hoechst Yellow 73
Hansa Brilliant Yellow 5GX-02
Hoechst Yellow 74
Dalamar .RTM. Yellow YT-858-D
Heubach Yellow 74
Hansa Yellow X Hoechst Yellow 75
Novoperm .RTM. Yellow HR
Hoechst Yellow 83
Chromophtal .RTM. Yellow 3G
Ciba-Geigy Yellow 93
Chromophtal .RTM. Yellow GR
Ciba-Geigy Yellow 95
Novoperm .RTM. Yellow FGL
Hoechst Yellow 97
Hansa Brilliant Yellow 10GX
Hoechst Yellow 98
Permanent Yellow G3R-01
Hoechst Yellow 114
Chromophtal .RTM. Yellow 8G
Ciba-Geigy Yellow 128
Irgazin .RTM. Yellow 5GT
Ciba-Geigy Yellow 129
Hostaperm .RTM. Yellow H4G
Hoechst Yellow 151
Hostaperm .RTM. Yellow H3G
Hoechst Yellow 154
L74-1357 Yellow Sun Chem.
L75-1331 Yellow Sun Chem.
L75-2377 Yellow Sun Chem.
Hostaperm .RTM. Orange GR
Hoechst Orange 43
Paliogen .RTM. Orange
BASF Orange 51
Irgalite .RTM. Rubine 4BL
Ciba-Geigy Red 57:1
Quindo .RTM. Magenta
Mobay Red 122
Indofast .RTM. Brilliant Scarlet
Mobay Red 123
Hostaperm .RTM. Scarlet GO
Hoechst Red 168
Permanent Rubine F6B
Hoechst Red 184
Monastral .RTM. Magenta
Ciba-Geigy Red 202
Monastral .RTM. Scarlet
Ciba-Geigy Red 207
Heliogen .RTM. Blue L 6901F
BASF Blue 15:2
Heliogen .RTM. Blue NBD 7010
BASF
Heliogen .RTM. Blue K 7090
BASF Blue 15:3
Heliogen .RTM. Blue L 7101F
BASF Blue 15:4
Paliogen .RTM. Blue L 6470
BASF Blue 60
Heucophthal .RTM. Blue G, XBT-583D
Heubach Blue 15:3
Heliogen .RTM. Green K 8683
BASF Green 7
Heliogen .RTM. Green L 9140
BASF Green 36
Monastral .RTM. Violet R
Ciba-Geigy Violet 19
Monastral .RTM. Red B
Ciba-Geigy Violet 19
Quindo .RTM. Red R6700
Mobay Violet 19
Quindo .RTM. Red R6713
Mobay Violet 19
Indofast .RTM. Violet
Mobay Violet 23
Monastral .RTM. Violet Maroon B
Ciba-Geigy Violet 42
Monarch .RTM. 1400 Cabot Black 7
Monarch .RTM. 1300 Cabot Black 7
Monarch .RTM. 1100 Cabot Black 7
Monarch .RTM. 1000 Cabot Black 7
Monarch .RTM. 900 Cabot Black 7
Monarch .RTM. 880 Cabot Black 7
Monarch .RTM. 800 Cabot Black 7
Monarch .RTM. 700 Cabot Black 7
Raven 7000 Columbian Black 7
Raven 5750 Columbian Black 7
Raven 5250 Columbian Black 7
Raven 5000 Columbian Black 7
Raven 3500 Columbian Black 7
Color Black FW 200 Degussa Black 7
Color Black FW 2 Degussa Black 7
Color Black FW 2V Degussa Black 7
Color Black FW 1 Degussa Black 7
Color Black FW 18 Degussa Black 7
Color Black S 160 Degussa Black 7
Color Black S 170 Degussa Black 7
Special Black 6 Degussa Black 7
Special Black 5 Degussa Black 7
Special Black 4A Degussa Black 7
Special Black 4 Degussa Black 7
Printex U Degussa Black 7
Printex V Degussa Black 7
Printex 140U Degussa Black 7
Printex 140V Degussa Black 7
Tipure .RTM. R-101 Du Pont White 6
______________________________________
Representative commercial pigments that can be used in the form of a water
wet presscake include: Heucophthal.RTM. Blue BT-585-P, Toluidine Red Y
(C.I. Pigment Red 3), Quindo.RTM. Magenta (Pigment Red 122), Magenta
RV-6831 presscake (Mobay Chemical, Harmon Division, Haledon, N.J.),
Sunfast.RTM. Magenta 122 (Sun Chemical Corp., Cincinnati, Ohio), Indo.RTM.
Brilliant Scarlet (Pigment Red 123, C.I. No. 71145), Toluidine Red B (C.I.
Pigment Red 3), Watchung.RTM. Red B (C.I. Pigment Red 48), Permanent
Rubine F6B13-1731 (Pigment Red 184), Hansa.RTM. Yellow (Pigment Yellow
98), Dalamaro.RTM. Yellow YT-839-P (Pigment Yellow 74, C.I. No. 11741,
Sunbrite.RTM. Yellow 17 (Sun Chemical Corp, Cincinnati, Ohio), Toluidine
Yellow G (C.I. Pigment Yellow 1), Pigment Scarlet (C.I. Pigment Red 60),
Auric Brown (C.I. Pigment Brown 6), etc. Black pigments, such as carbon
black, generally are not available in the form of aqueous presscakes.
Fine particles of metal or metal oxides also may be used to practice the
invention. For example, metal and metal oxides are suitable for the
preparation of magnetic ink jet inks. Fine particle size oxides, such as
silica, alumina, titania, and the like, also may be selected. Furthermore,
finely divided metal particles, such as copper, iron, steel, aluminum and
alloys, may be selected for appropriate applications.
Dyes
Dyes commonly used in aqueous ink jet inks include for example Acid,
Direct, Food and Reactive dyes.
Amongst useful dyes there may be mentioned:
C.I. Food Black 1
C.I. Food Black 2
C.I. Acid Black 7
C.I. Acid Black 24
C.I. Acid Black 26
C.I Acid Black 48
C.I. Acid Black 52
C.I Acid Black 58
C.I. Acid Black 60
C.I Acid Black 107
C.I. Acid Black 109
C.I. Acid Black 118
C.I. Acid Black 119
C.I. Acid Black 131
C.I. Acid Black 140
C.I. Acid Black 155
C.I. Acid Black 156
C.I. Acid Black 187
C.I. Direct Black 17
C.I. Direct Black 19
C.I. Direct Black 32
C.I. Direct Black 38
C.I. Direct Black 51
C.I. Direct Black 71
C.I. Direct Black 74
C.I. Direct Black 75
C.I. Direct Black 112
C.I. Direct Black 117
C.I. Direct Black 154
C.I. Direct Black 163
C.I. Direct Black 168
C.I. Acid Red 1
C.I. Acid Red 8
C.I. Acid Red 17
C.I. Acid Red 32
C.I. Acid Red 35
C.I. Acid Red 37
C.I. Acid Red 42
C.I. Acid Red 57
C.I. Acid Red 92
C.I. Acid Red 115
C.I. Acid Red 119
C.I. Acid Red 131
C.I. Acid Red 133
C.I. Acid Red 134
C.I. Acid Red 154
C.I. Acid Red 186
C.I. Acid Red 249
C.I. Acid Red 254
C.I. Acid Red 256
C.I. Direct Red 37
C.I. Direct Red 63
C.I. Direct Red 75
C.I. Direct Red 79
C.I. Direct Red 80
C.I. Direct Red 83
C.I. Direct Red 99
C.I. Direct Red 220
C.I. Direct Red 224
C.I. Direct Red 227
C.I. Acid Violet 11
C.I. Acid Violet 34
C.I. Acid Violet 75
C.I. Direct Violet 47
C.I. Direct Violet 48
C.I. Direct Violet 51
C.I. Direct Violet 90
C.I. Direct Violet 94
C.I. Reactive Red 4
C.I. Reactive Red 23
C.I. Reactive Red 24
C.I. Reactive Red 31
C.I. Reactive Red 56
C.I. Acid Blue 9
C.I. Acid Blue 29
C.I. Acid Blue 62
C.I. Acid Blue 102
C.I. Acid Blue 104
C.I. Acid Blue 113
C.I. Acid Blue 117
C.I. Acid Blue 120
C.I. Acid Blue 175
C.I. Acid Blue 183
C.I. Direct Blue 1
C.I. Direct Blue 6
C.I. Direct Blue 8
C.I. Direct Blue 15
C.I. Direct Blue 25
C.I. Direct Blue 71
C.I. Direct Blue 76
C.I. Direct Blue 78
C.I. Direct Blue 80
C.I. Direct Blue 86
C.I. Direct Blue 90
C.I. Direct Blue 106
C.I. Direct Blue 108
C.I. Direct Blue 123
C.I. Direct Blue 163
C.I. Direct Blue 165
C.I. Direct Blue 199
C.I. Direct Blue 226
C.I. Reactive Blue 7
C.I. Reactive Blue 13
C.I. Acid Yellow 3
C.I. Acid Yellow 17
C.I. Acid Yellow 19
C.I. Acid Yellow 23
C.I. Acid Yellow 25
C.I. Acid Yellow 29
C.I. Acid Yellow 38
C.I. Acid Yellow 49
C.I. Acid Yellow 59
C.I. Acid Yellow 61
C.I. Acid Yellow 72
C.I. Direct Yellow 27
C.I. Direct Yellow 28
C.I. Direct Yellow 33
C.I. Direct Yellow 39
C.I. Direct Yellow 58
C.I. Direct Yellow 86
C.I. Direct Yellow 100
C.I. Direct Yellow 142
C.I. Reactive Yellow 2.
AQUEOUS CARRIER MEDIUM
The aqueous carrier medium is water or a mixture of water and at least one
water soluble organic solvent other than the penetrant.
Deionized water is commonly used. Selection of a suitable mixture of water
and water soluble organic solvent, depends on requirements of the specific
application, such as desired surface tension and viscosity, the selected
pigment, drying time of the pigmented ink jet ink, and the type of paper
onto which the ink will be printed.
Representative examples of water-soluble organic solvents that may be
selected include (1) alcohols, such as methyl alcohol, ethyl alcohol,
n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol,
t-butyl alcohol, iso-butyl alcohol, furfuryl alcohol, and
tetrahydrofurfuryl alcohol; (2) ketones or ketoalcohols such as acetone,
methyl ethyl ketone and diacetone alcohol; (3) ethers, such as
tetrahydrofuran and dioxane; (4) esters, such as ethyl acetate, ethyl
lactate, ethylene carbonate and propylene carbonate; (5) polyhydric
alcohols, such as ethylene glycol, diethylene glycol, triethylene glycol,
propylene glycol, tetraethylene glycol, polyethylene glycol, glycerol,
2-methyl-2,4-pentanediol, 1,2,6-hexanetriol and thiodiglycol; (6) lower
alkyl mono- or di-ethers derived from alkylene glycols, such as ethylene
glycol mono-methyl (or -ethyl) ether, diethylene glycol mono-methyl (or
-ethyl) ether, propylene glycol mono-methyl (or -ethyl) ether, triethylene
glycol mono-methyl (or -ethyl) ether and diethylene glycol di-methyl (or
-ethyl) ether; (7) nitrogen containing cyclic compounds, such as
pyrrolidone, N-methyl-2-pyrrolidone, and 1,3-dimethyl-2-imidazolidinone;
and (8) sulfur-containing compounds such as dimethyl sulfoxide and
tetramethylene sulfone.
A mixture of a water soluble organic solvent having at least 2 hydroxyl
groups such as, diethylene glycol and water is preferred as the aqueous
carrier medium. In the case of a mixture of water, diethylene glycol and
penetrant, the aqueous carrier medium plus penetrant usually contains from
about 30% water/70% solvent/penetrant mixture to about 95% water/5%
solvent/penetrant mixture. The preferred ratios are approximately 60%
water/40% solvent/penetrant mixture to about 95% water/5%
solvent/penetrant mixture. The solvent/penetrant mixture contains 15-95%
penetrant, preferably 25-75%.
Percentages are based on the total weight of the aqueous carrier medium
plus penetrant.
OTHER INGREDIENTS
The ink may contain other ingredients. For example, surfactants may be used
to alter surface tension as well as promote penetration. However, they may
also destabilize pigmented inks. Surfactants may be anionic, cationic,
amphoteric or nonionic. Useful surfactants may be selected from
McCutcheon's Emulsifiers and Detergents, published by Manufacturing
Confectioners Publishing Company, Glen Rock, N.J. The choice of surfactant
is highly dependent on the type of paper to be printed. It is expected
that one skilled in the art can select the appropriate surfactant for the
specific paper to be used in printing.
For example, the following surfactants were found to be useful in printing
on Gilbert Bond paper (25% cotton) designated style 1057 manufactured by
Mead Company, Dayton, Ohio.
______________________________________
Supplier and Tradename
Description
______________________________________
Air Products
Surfynol .RTM. 465H
Ethoxylated Tetramethyl
Decynediol
Surfynol .RTM. CT-136
Acethylenic Diol,
Anionic Surfactant
Blend
Surfynol .RTM. GA Acetylenic Diol Blend
Surfynol .RTM. TG Acetylenic Diol Blend
in Ethylene Glycol
Cyanamid
Aerosol .RTM. OT Dioctyl Ester of Sodium
Sulfosuccinic Acid
Aerosol .RTM. MA-80
Dihexyl Ester of
Sodium Sulfosuccinic
Acid Aerosol .RTM. MA-
80/Aerosol OT 2/1
Du Pont
Duponol .RTM. RA Fortified Sodium Ether-
Alcohol Sulfate
Merpol .RTM. A Ethylene Oxide, Ester
Condensate
Merpol .RTM. LF-H Polyether
Merpol .RTM. SE Alcohol Ethoxylate
Merpol .RTM. SH Ethylene Oxide Condensate
Zelec .RTM. NK Alcohol Phosphate
Composition
Fisher Scientific
Polyethylene Glycol 3350
Polyethylene Glycol 400
Polyethylene Glycol 600
ICI
Renex .RTM. 30 Polyoxyethylene (12)
Tridecyl Ether
Synthrapol .RTM. KB
Polyoxyethylene Alkyl
Alcohol
Rohm & Haas
Triton .RTM. CF 10 Alkylaryl Polyether
Triton .RTM. CF 21 Alkylaryl Polyether
Triton .RTM. N 111 Nonylphenoxy
Polyethoxy Ethanol
Triton .RTM. X 102 Octylphenoxy
Polyethoxy
Ethanol
Triton .RTM. X 114 Octylphenoxy
Polyethoxy
Ethanol
Union Carbide
Silwet .RTM. L-7600
Polyalkyleneoxide
Modified
Polydimethylsiloxane
Silwet .RTM. L-7607
Polyalkyleneoxide
Modified
Polydimethylsiloxane
Polyalkyleneoxide
Silwet .RTM. L-77 Modified
Polydimethylsiloxane
UCON .RTM. ML1281 Polyalkylene Glycol
W. R. Grace
Hampshire Div., Hamposyl .RTM. Lida
Lauryoyl
Iminodiacetic
Acid.
______________________________________
In aqueous inks, the surfactants may be present in the amount of 0.01-5%
and preferably 0.2-2%.
Biocides may be present to inhibit growth of microorganisms. Dowicides (Dow
Chemical, Midland MI), Omidines (Olin Corp.), Nopcocides (Henkel Corp.)
and sodium benzoate may be used.
In addition, sequestering agents such as EDTA may also be included to
eliminate deleterious effects of heavy metal impurities.
INK PREPARATION
The pigmented ink is prepared by premixing the selected pigment(s) and
acrylic block copolymer in water. In the case of dyes some of the same
factors apply except that there is no dispersant present and no need for
pigment deaggregation. The dye-based ink is prepared in a well agitated
vessel rather than in dispersing equipment. Cosolvents and penetrant may
be present during the dispersion.
The dispersing step may be accomplished in a horizontal mini mill, a ball
mill, an attritor, or by passing the mixture through a plurality of
nozzles within a liquid jet interaction chamber at a liquid pressure of at
least 1000 psi to produce a uniform dispersion of the pigment particles in
the aqueous carrier medium.
It is generally desirable to make the pigmented ink jet ink in concentrated
form. The concentrated pigmented ink jet ink is subsequently diluted to
the appropriate concentration for use in the ink jet printing system. This
technique permits preparation of a greater quantity of pigmented ink from
the equipment. If the pigment dispersion is made in a solvent, it is
diluted with water and optionally other solvents to obtain the appropriate
concentration. If the pigment dispersion is made in water, it is diluted
with either additional water or water soluble solvents to make a pigment
dispersion of the desired concentration. By dilution, the ink is adjusted
to the desired viscosity, color, hue, saturation density, and print area
coverage for the particular application.
In the case of organic pigments, the ink may contain up to approximately
30% pigment by weight, but will generally be in the range of approximately
0.1 to 15%, preferably approximately 0.1 to 8%, by weight of the total ink
composition for most thermal ink jet printing applications. If an
inorganic pigment is selected, the ink will tend to contain higher weight
percentages of pigment than with comparable inks employing organic
pigment, and may be as high as approximately 75% in some cases, because
inorganic pigments generally have higher specific gravities than organic
pigments. The acrylic block polymer is present in the range of
approximately 0.1 to 30% by weight of the total ink composition,
preferably in the range of approximately 0.1% to 8%. If the amount of
polymer becomes too high, the ink color density will be unacceptable and
it will become difficult to maintain desired ink viscosity. Dispersion
stability of the pigment particles is adversely affected if insufficient
acrylic block copolymer is present. The amount of aqueous carrier medium
plus penetrant is in the range of approximately 70 to 99.8%, preferably
approximately 94 to 99.8%, based on total weight of the ink when an
organic pigment is selected, approximately 25 to 99.8%, preferably
approximately 70 to 99.8% when an inorganic pigment is selected and 80 to
99.8% when a dye is selected.
Other additives, such as surfactants, biocides, humectants, chelating
agents, and viscosity modifiers may be added to the ink. Optionally, other
acrylic and non-acrylic polymers, may be added to improve properties such
as water fastness and smear resistance.
Jet velocity, separation length of the droplets, drop size, and stream
stability are greatly affected by the surface tension and the viscosity of
the ink. Pigmented ink jet inks suitable for use with ink jet printing
systems should have a surface tension in the range of about 20 dyne/cm to
about 70 dyne/cm and, more preferably, in the range 30 dyne/cm to about 70
dyne/cm. Acceptable viscosities are no greater than 20 cP, and preferably
in the range of about 1.0 cP to about 10.0 cP. The ink has physical
properties compatible with a wide range of ejecting conditions, i.e.,
driving voltage and pulse width for thermal ink jet printing devices,
driving frequency of the piezo element for either a drop-on-demand device
or a continuous device, and the shape and size of the nozzle. The inks
have excellent storage stability for a long period and do not clog in an
ink jet apparatus. Fixing the ink on the image recording material, such
as, paper, fabric, film, etc., can be carried out rapidly and accurately.
The printed ink images have clear color tones, high density, excellent
water resistance and lightfastness. Furthermore, the ink does not corrode
parts of the ink jet printing device it comes in contact with, and it is
essentially odorless, and non-toxic.
The following examples serve to illustrate the practice of the present
invention.
EXAMPLES 1-7
All inks were prepared as follows:
Dispersant Preparation:
A block copolymer of n-butyl methacrylate and methacrylic acid was prepared
as follows:
3750 grams of tetrahydrofuran, 7.4 grams of p-xylene, were added to a
12-liter flask equipped with a mechanical stirrer, thermometer, nitrogen
inlet, drying tube outlet, and addition funnels. The catalyst, tetrabutyl
ammonium m-chlorobenzoate, and 3.0 ml of a 1.0 M solution in acetonitrile,
was then added to the flask. 291.1 grams (1.25 M) of an initiator,
1,1-bis(trimethyl-siloxy)-2-methyl propene, was injected. Feed I which
consisted of tetrabutyl ammonium m-chlorobenzoate, and 3.0 ml of a 1.0 M
solution in acetonitrile, was started and added over 150 minutes. Feed II
which consisted of 1976 gm (12.5M) trimethylsilyl methacrylate, was
started at 0.0 minutes and added over 35 minutes. One hundred and eighty
minutes after Feed II was completed over 99% of the monomers had reacted.
Feed III, which consisted of 1772 gm (12.5 M) butyl methacrylate, was
started and added over 30 minutes.
At 400 minutes, 780 grams of dry methanol was added to the above solution
and distillation commenced. During the first stage of distillation, 1300.0
grams of material with a boiling point below 55.degree. C. was removed
from the flask. The theoretical amount of methoxytrimethylsilane, having a
boiling point of 54.degree. C., (BP =54.degree. C.) to be removed was
1144.0 grams. Distillation continued during the second stage while the
boiling point increased to 76.degree. C. Isopropanol, 5100 gms, was added
during the second stage of distillation. A total of 7427 grams of solvent
were removed. The resultant resin solution was used directly in the next
step. It contained 55.8% solids and had a neutralization equivalent of
4.65 milliequivalents of potassium hydroxide per gram of solids.
Neutralization of Dispersant:
The following materials were added to a 1000 ml cylindrical polyethylene
bottle:
200.0 grams dispersant solution
174.4 grams 15% potassium hydroxide
137.6 grams deionized water
The mixture was tumbled on a roller mill for 3-4 hours and then
magnetically stirred for 16-20 hours to give a slightly cloudy solution.
Preparation of Pigment Dispersion:
The following materials were added to a 1 liter beaker:
78.3 grams deionized water
66.7 grams neutralized dispersant solution
3.0 grams 15% potassium hydroxide
The solution was mechanically stirred while 20.0 grams of carbon black
pigment, FW 18 (Degussa Corp., Ridgefield Park, N.J. 07660) was added in
portions. Stirring was continued for 30 minutes. The contents were then
added to a Mini Motormill 100 (Eiger Machinery Inc., Bensenville, Ill.
60106) with another 32 grams of deionized water as a rinse. The contents
were milled at 3500 rpm for one hour. The yield was 190.8 grams. The pH
was 7.6. The particle size was 138 nm as determined by a Brookhaven BI-90
Particle analyzer (Brookhaven Instruments Corp., Holtsville, N.Y. 11742).
Preparation of Inks:
The following ingredients were combined and added with magnetic stirring
over 10-15 minutes to 22.5 grams of pigment dispersion:
2.6 grams diethylene glycol (Aldrich Chemical Co. Inc., Milwaukee, Wis.
53233)
2.6 grams comparative cosolvent or diol penetrant
0.5 grams Silwet.RTM. L-77 (Union Carbide Corp., Danbury, Conn. 06817)
37.2 grams deionized water.
TABLE 1
Control Cosolvent And Diol Penetrant Identification
All cosolvents and diol penetrants were obtained from Aldrich Chemical Co.
Inc., Milwaukee, Wis. 53233 unless otherwise stated. A cosolvent or diol
penetrant was added to the ink as previously discussed. The cosolvents and
diol penetrants are identified as follows:
______________________________________
Comparative
Cosolvents Control #
______________________________________
Butyl Carbitol (Union Carbide
1
Copr., Danbury, CT 06817)
Dowanol TBH, (Dow Chemical,
2
Midland MI 48640)
Dipropylene Glycol 3
Hexylene Glycol 4
Neopentyl Glycol 5
Triethylene Glycol 6
Glycerol 7
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Diol Penetrants Example #
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2-Ethyl-2-methyl-1,3-propanediol
1
3,3-Dimethyl-1,2-butanediol
2
2,2-Diethyl-1,3-propanediol
3
2-Methyl-2-propyl-1,3-propanediol
4
2,4-Dimethyl-2,4-pentanediol
5
2,5-Dimethyl-2,5-hexanediol
6
5-Hexene-1,2-diol 7
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TABLE 2
Drying Times
Drying times were obtained by printing rapidly a series of solid patterns
on a Hewlett Packard DeskJet printer (Hewlett Packard Co., Palo Alto,
Calif. 94303) and immediately wiping them in 15 second increments, and
recording the time in which the printed ink would no longer smear. A
semiabsorbent paper, Gilbert Bond (Mead Co., Dayton, Ohio) was used.
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Sample Dry Time, seconds
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Control 1 <15
Control 2 <15
Control 3 15-30
Control 4 15-30
Control 5 15-30
Control 6 15-30
Control 7 30-45
Example 1 <15
2 <15
3 <15
4 <15
5 <15
6 <15
7 <15
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Dispersion stability was obtained by subjecting 15 grams of ink to four
temperature cycles, each consisting of 4 hours at -20.degree. C. and 4
hours at 60.degree. C. Particle sizes were measured on a Brookhaven BI-90
(Brookhaven Instruments Corp., Holtsville, N.Y. 11742) before and after
cycling.
TABLE 3
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Dispersion Stability
Change in Particle Size, delta
Sample nanometers
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Control 1 36
2 22
3 4
4 2
5 4
6 3
7 -5
Example 1 3
2 4
3 17
4 7
5 0
6 6
7 12
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TABLE 4
Crust Times
Crust times were obtained on a Deskjet printer that had been altered so
that the ink cartridge would not be vacuum suctioned nor spit into a
spittoon. The last time interval that the particular drop did not fail is
recorded.
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5th 32nd Drop
Sample 1st seconds minutes
minutes
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Control 1 90 1 1.5
2 60 1 3.0
3 55 2 5.0
4 40 0.5 1.5
5 35 1 1.5
6 40 1 1.1
7 25 0.75 1.0
Example 1 70 1.0 2.0
2 60 1.3 2.5
3 60 1.3 15
4 55 1.6 4.5
5 45 0.5 10
6 40 1.1 20
7 45 1.0 1.5
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TABLE 5
Optical Densities
Optical densities were obtained on the print side as well as the backside
of the paper using a Macbeth RD 918 Densitometer (Macbeth).
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Print Strikethrough
or Front
or Back
Sample Density Units
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Control 1 1.05 0.17
2 1.05 0.17
3 * *
4 1.10 0.11
5 1.22 0.11
6 1.30 0.12
7 1.38 0.12
Example 1 1.09 0.11
2 1.05 0.17
3 1.05 0.16
4 1.13 0.18
5 1.09 0.13
6 1.13 0.12
7 1.16 0.12
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* Printed poorly in solid patterns so that reliable data could not be
obtained.
The best situation maximizes front density and back density where small
drop volumes will produce dots that spread to maximum area. Spreading is
maximized when back densities are 0.16-0.18.
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